1. Field of the Invention
The present invention relates to an acoustic sensor, a manufacturing method for the acoustic sensor, and a semiconductor electret condenser microphone using the acoustic sensor.
2. Description of the Related Art
The electret condenser microphone is widely used in mobile telephones because it is easily reduced in size. An example of an art-known electret condenser microphone is shown in FIG. 10. This electret condenser microphone includes a case 1, a diaphragm 7 provided in this case 1, an electret film 5 (formed in the case 1) disposed opposite to this diaphragm 7, and an amplifying element 9 for amplifying the change of voltage due to change of electrostatic capacity of the capacitor composed of the diaphragm 7 and electret film 5. The amplifying element 9 is incorporated in the case 1.
For a conventional electret condenser microphone, the components for the amplifying element and the capacitor are completely separate, and there is a limit to reduction of sizes.
For this kind of electret condenser microphone, in particular, since an independent FET was used for impedance conversion, reduction of size was difficult.
The present invention was designed in the light of the problems associated with the prior art, and an object of the invention was to develop an acoustic sensor capable of substantially reducing the size of the semiconductor electret condenser microphone, a manufacturing method for the acoustic sensor, and a semiconductor electret condenser microphone using the acoustic sensor.